Formation of sedimentary structures in flume experiments under upper-flow-regime conditions

点击翻译按钮获取中文摘要

In an attempt to produce plane beds under upper-flow-regime conditions, we have conducted a number of runs (experiments) using a hydraulic flume of 15 cm wide and 700 cm long, at the Ocean Research Institute, University of Tokyo. We have succeeeded in producing two types of plane beds : 1) laminae formed and buried by the migration of low-relief asymmetric ripples under near- or sub-critical flow (Froude Number Fr=0.94 ; type 1), and 2) laminae formed without causing any low-relief bedform but under super-critical flow (Fr=1.98 ; type 2). After making these two types of plane beds, imbrication of detrital grains along each plane bed was investigated. The sediments of sand-sized quartz grains (mean diameter 0.72 mm) show a high angle of imbrication (up to 30ﾟ) in type 2, whereas very low angle of imbrication (close to 0ﾟ) in type 1. Differences of imbrication angle between the two types of plane bed may be useful to infer the individual formational process of plane beds that are observed in the field.